3 ms·

Whatever the speed, they won't have the capacity that mass transit provides in things like London underground.

Silhouette 11y ago
That depends very much on the design. Remember that at any given time, most of the tunnel in the Underground is empty. Most of the time you're waiting in stations is because other people are getting on or off, not you or your own party. And most of the stations you stop at (and travel slower before and after) aren't relevant to your own journey. A network of high speed paths with efficient out-of-path access for starting and ending journeys could in principle offer dramatically higher throughput than current mass transit on the Underground, even with individuals or small groups sharing private vehicles. The trouble is that the amount of time and money required to build that network underground would be staggering even under ideal conditions, and conditions under London are very far from ideal.
- Symbiote 11y ago
  But the bits of tunnel that aren't empty are extremely full. A tube train carries over 1000 people maximum. But it also takes up about 1km of track before the next train (estimated since stations are about 10 minutes walk apart). We have 1 person per metre of tunnel. The platform is roughly the length of the train, 130m. A small cart carrying one person could be, say, 1.5m long, and take up 3m (very optimistic, I think). Now we only have ⅓ person per metre of tunnel. Let's say 200 people get on or off the train at a busy station. There's a train every 120 seconds. The additional space is slightly larger than the train (the platform). If it takes 10s to get off the cart, in 120s we can load/unload 12 carts. But they're smaller, so we can do, say, 75 in the existing platform space (130m). That's 900, so this bit isn't a problem. Maybe it adds up; I'm actually far to tired to continue working it out...
  - Silhouette 11y ago
    Sorry, but I don't think some of your assumptions make much sense. Tube train tunnels are large. If we were developing some alternative method of transport, why would we reserve the entire cross section of current tunnels for single occupancy vehicles? As demonstrated by the Tube itself, much higher densities could be achieved, even with private vehicles, either by having multiple people per vehicle or by using smaller vehicles that didn't require as much space and could run alongside others. Of course density isn't the only thing that matters. Consider that the average speed of an Underground train is about 20mph. A fit person can run faster than a Tube train moves over short distances.[1] Clearly if you had a system where loading and unloading happened without blocking the main tunnels, significantly higher speeds could be achieved over the kinds of distances a typical passenger might be travelling. [1] No, really! https://www.youtube.com/watch?v=PH_Z8Ghuq6E https://www.youtube.com/watch?v=PH_Z8Ghuq6E
    - lorenzhs 11y ago
      Tube tunnels relay are not large. They vary a bit by line but in general they're really really small and severely limit the design of new trains. There's no way you'd fit two vehicles side by side in those tunnels, and they're not high enough to stack them either. Nor are they interconnected well enough to make one the passing lane. Have a look for yourself if you get to London, the entire tube system is mind-boggling.
      - Silhouette 11y ago
        I'm from the UK and have been riding the Tube for decades. If we're talking about a hypothetical alternative transport system to be built underground and carry private vehicles potentially with single occupancy, you could probably fit four such vehicles within a cross sectional area not much bigger than the existing tunnels. The engineering practicalities would presumably still favour a round tunnel, which would be less efficient in space if you were running smaller vehicles in parallel, though. Then again, as I mentioned elsewhere, the cost of actually doing any of this in both time and money would be wildly prohibitive today and seems likely to remain so for many years to come, so this is all rather hypothetical anyway.
        lorenzhs 11y ago
        Right, sorry. If the tunnels were even 30cm wider this would indeed be a lot simpler, but as you say the cost of that would be wildly prohibitive in the foreseeable future. TfL would love it, though ;) Come to think about it, what would be the optimal layout of such an underground tunnel system for single-occupancy vehicles? The current system of changing lines and the station layout that results from it would no longer be a good fit, you'd have to come almost to a standstill. It could even be that reusing the tube tunnels would be less efficient than boring new tunnels in a future where tunnels can be bored "cheaply" with very little human involvement.
        Symbiote 11y ago
        Are tunnels likely to get much cheaper? Compared to a lot of construction work it seems to be fairly automated already — take a look at some Crossrail videos [1] — so I'll bet a lot of the cost is design, planning and solving unexpected problems. And the cost of the machine. [1] https://youtu.be/X_ffeK8SIDo?list=PLF8E85417123BEF2F&t=66 https://youtu.be/X_ffeK8SIDo?list=PLF8E85417123BEF2F&t=66 (Quotes, roughly: 500,000 components in the tunnel boring machine, staff of 20 round the clock,

That depends very much on the design. Remember that at any given time, most of the tunnel in the Underground is empty. Most of the time you're waiting in stations is because other people are getting on or off, not you or your own party. And most of the stations you stop at (and travel slower before and after) aren't relevant to your own journey. A network of high speed paths with efficient out-of-path access for starting and ending journeys could in principle offer dramatically higher throughput than current mass transit on the Underground, even with individuals or small groups sharing private vehicles. The trouble is that the amount of time and money required to build that network underground would be staggering even under ideal conditions, and conditions under London are very far from ideal.

Symbiote 11y ago
But the bits of tunnel that aren't empty are extremely full. A tube train carries over 1000 people maximum. But it also takes up about 1km of track before the next train (estimated since stations are about 10 minutes walk apart). We have 1 person per metre of tunnel. The platform is roughly the length of the train, 130m. A small cart carrying one person could be, say, 1.5m long, and take up 3m (very optimistic, I think). Now we only have ⅓ person per metre of tunnel. Let's say 200 people get on or off the train at a busy station. There's a train every 120 seconds. The additional space is slightly larger than the train (the platform). If it takes 10s to get off the cart, in 120s we can load/unload 12 carts. But they're smaller, so we can do, say, 75 in the existing platform space (130m). That's 900, so this bit isn't a problem. Maybe it adds up; I'm actually far to tired to continue working it out...
- Silhouette 11y ago
  Sorry, but I don't think some of your assumptions make much sense. Tube train tunnels are large. If we were developing some alternative method of transport, why would we reserve the entire cross section of current tunnels for single occupancy vehicles? As demonstrated by the Tube itself, much higher densities could be achieved, even with private vehicles, either by having multiple people per vehicle or by using smaller vehicles that didn't require as much space and could run alongside others. Of course density isn't the only thing that matters. Consider that the average speed of an Underground train is about 20mph. A fit person can run faster than a Tube train moves over short distances.[1] Clearly if you had a system where loading and unloading happened without blocking the main tunnels, significantly higher speeds could be achieved over the kinds of distances a typical passenger might be travelling. [1] No, really! https://www.youtube.com/watch?v=PH_Z8Ghuq6E https://www.youtube.com/watch?v=PH_Z8Ghuq6E
  - lorenzhs 11y ago
    Tube tunnels relay are not large. They vary a bit by line but in general they're really really small and severely limit the design of new trains. There's no way you'd fit two vehicles side by side in those tunnels, and they're not high enough to stack them either. Nor are they interconnected well enough to make one the passing lane. Have a look for yourself if you get to London, the entire tube system is mind-boggling.
    - Silhouette 11y ago
      I'm from the UK and have been riding the Tube for decades. If we're talking about a hypothetical alternative transport system to be built underground and carry private vehicles potentially with single occupancy, you could probably fit four such vehicles within a cross sectional area not much bigger than the existing tunnels. The engineering practicalities would presumably still favour a round tunnel, which would be less efficient in space if you were running smaller vehicles in parallel, though. Then again, as I mentioned elsewhere, the cost of actually doing any of this in both time and money would be wildly prohibitive today and seems likely to remain so for many years to come, so this is all rather hypothetical anyway.
      - lorenzhs 11y ago
        Right, sorry. If the tunnels were even 30cm wider this would indeed be a lot simpler, but as you say the cost of that would be wildly prohibitive in the foreseeable future. TfL would love it, though ;) Come to think about it, what would be the optimal layout of such an underground tunnel system for single-occupancy vehicles? The current system of changing lines and the station layout that results from it would no longer be a good fit, you'd have to come almost to a standstill. It could even be that reusing the tube tunnels would be less efficient than boring new tunnels in a future where tunnels can be bored "cheaply" with very little human involvement.
        Symbiote 11y ago
        Are tunnels likely to get much cheaper? Compared to a lot of construction work it seems to be fairly automated already — take a look at some Crossrail videos [1] — so I'll bet a lot of the cost is design, planning and solving unexpected problems. And the cost of the machine. [1] https://youtu.be/X_ffeK8SIDo?list=PLF8E85417123BEF2F&t=66 https://youtu.be/X_ffeK8SIDo?list=PLF8E85417123BEF2F&t=66 (Quotes, roughly: 500,000 components in the tunnel boring machine, staff of 20 round the clock,